Testosterone and 5HIAA in dogs with intraspecific aggression

Abstract

Intraspecific aggression is a common problem in dogs, with such aggression typically due to dominance, fear, and/or territoriality. Some dogs appear to perceive the mere presence of another dog as a challenge or threat. These dogs often show serious, unprovoked aggression characterized by phenotypically dominant postures, and this aggression may even result in a lethal injury to the other dog. Studies in humans and various animal species have demonstrated links between androgens such as testosterone, dehydroepiandrosterone sulfate (DHEAS), androstenedione (AE); social status; and aggression. Additionally, similar links have been made between serotonin (5-HT) levels, where subjects with low serotonin levels show higher levels of aggression and impulsivity and lower social status compared to those with higher levels of serotonin. This study was performed to determine if inappropriate aggression in dogs could be associated with high androgen levels and low serotonin levels as compared to control dogs. Seven aggressive female dogs were age- and size-matched to normal controls. Blood was gathered for assessment of testosterone, DHEAS, AE, 5-HT, and 5-hydroxyindoleacetic acid (5-HIAA). Serotonin and 5-HIAA were analyzed by a Wilcoxan Signed Rank Test. Androgens were evaluated by a one-sided paired t-test. Testosterone levels were below detectable limits in all dogs tested. No significant difference was found in the mean levels of DHEA and AE between control and aggressive dogs. Similarly no significant difference was observed in median levels of 5-HT and 5-HIAA between control and aggressive dogs. A significant difference was noted in the 5-HIAA/5-HT ratio but in the direction opposite of that expected - the ratio was higher in aggressive dogs than control dogs.